Studies are being conducted to characterize central and periferal reflex modulation of renin and blood pressure. In particular, a series of studies is being conducted to examine hypothalamic modification of renin control in instrumented, free-running dogs. Other studies are being conducted to study mechanisms whereby renin is elevated during respiratory acidosis. The isolated influences of the adrenals, the renal sympathetic nerves and renal tubular components are being examined. Isolated effects of peripheral and central chemoreceptors on renin mechanisms are also being studied in anesthetized dogs. Other studies examining central modification of renin during maneuvers known reflexively to stimulate renin secretion are being conducted.